1. Field of the Invention
The present invention relates to an ultrasonic crack discovering apparatus for hunting cracks generated in a tube such as cracks occurring in welded portions of a boiler steel tube, from inside the tube.
2. Prior Art
With regard to boiler steel pipes, since generally a large number of steel tubes are arrayed within a boiler very close to one another, welded portions of boiler steel tubes, where occurrence of cracks are feared, have been almost not accessible for the purpose of crack hunting. Consequently, in the prior art, after the boiler steel tubes in a panel form had been carried to the outside of a boiler by spending a lot of man-hours, the welded portions were ground and magnetic-powder crack hunting was carried out on the ground portions.
As described above, in the prior art, an inspection of welded portions (especially welded portions with spacers) of boiler steel tubes was almost unable to be executed with the boiler in its original state because of a narrow space for access to the welded portions.
Therefore, the boiler steel tubes were cut out for each panel and carried to the outside of a furnace with a crane, and grinding and subsequent magnetic-powder crack hunting were performed outside the furnace. And after finishing the inspection, the panel was carried into the furnace again with a crane, and welding was performed to restore the boiler to its original state. Howver, since the work necessitates enormous man-hours, its cost was high, and hence, the establishment of a simple and convenient alternative method to be employed has been desired.